Color-proofing is the procedure used by the printing industry for creating representative images that replicate the appearance of printed images without the cost and time required to actually set up a high-speed, high-volume printing press to print an example of the images intended. One such color proofer is a lathe bed scanner which utilizes a thermal printer having half-tone capabilities. This printer is arranged to form an image on a thermal print medium, or writing element, in which a donor transfers a dye to the thermal print medium upon a sufficient amount of thermal energy. This printer includes a plurality of diode lasers which can be individually modulated to supply energy to selected areas of the medium in accordance with an information signal. The printhead of the printer includes one end of a fiber optic array having a plurality of optical fibers coupled to the diode lasers. The thermal print medium is supported on a rotatable imaging drum, and the printhead with the fiber optic array is movable relative to the longitudinal axis of the drum. The dye is transferred to the thermal print medium as the radiation, transferred from the diode lasers to the donor element by the optical fibers, is converted to thermal energy in the donor element.
For permitting relative movement of the printhead, the printhead is mounted on a translation table which, in turn, is attached to a rotatable lead screw having a threaded shaft. The lead screw rests between two sides of the frame of the scanner where it is supported on both ends by hearings. At the drive end, the lead screw continues through the bearing, through a pair of spring retainers that are separated and loaded by a compression spring and to a drive motor. The drive motor induces rotation to the screw, and the compression spring functions to limit axial movement of the lead screw.
The printhead moves in accordance with the translation table which, in turn, moves axially along translational rod bearings in register with the media during the write process. To ensure proper image quality, the movement of the table, and hence the printhead, must be precise and smooth. To achieve smooth translation, the current systems make use of bearing pads embedded in the bottom of the translation table that make contact with the translational rod bearings thereby reducing friction between the table and the bearing shafts. These pads are made from a commercially available plastic Delrin.TM. and the bearings are made from AISI 400 series stainless steel. This bearing apparatus is inadequate because it has significant friction which results in premature wear and consequently costly service and calibration.
There have been numerous attempts to solve the above friction and wear problems. For instance, U.S. Pat. No. 4,764,036 discloses tungsten carbide (WC) radial bearing or thrust inserts. The entire assembly is used as a hydrodynamic bearing in contrast to our invention as frictionless or rather low friction slide bearing. Further, U.S. Pat. No. 4,522,453 relates to the use of PVD (physical vapor deposition) and CVD (chemical vapor deposition) coatings comprising borides, nitrides and carbides as corrosion resistant as well as protection against high temperature wear. Moreover, U.S. Pat. No. 4,404,598 describes construction of engraving machines comprising lightweight lathe bed configurations. Low coefficient of friction Nylatron.TM. plastic pads are used on which rides the carriage.
Although the presently known and utilized scanner is satisfactory, it is not without shortcomings. The Delrin.TM. pads and the translational rod bearings are subjected to wear and abrasion and consequently require frequent maintenance and replacement. This is obviously labor intensive, time consuming and expensive.
Consequently, a need exists for improvements in the construction of the lathe bed scanner so as to overcome the above-described shortcomings.